1. Technical Field
This invention relates to measuring and testing apparatus and methods therefor. More particularly, the invention relates to shock testing apparatus and methods of operation designed to stimulate pyrotechnic shock (high g accelerations short duration) conditions.
2. Description of Related Art
Pyrotechnic shock testing involves applying high energy forces to electronic or mechanical components or subsystems prior to installation in commercial or military equipment. The forces provide the component with accelerations of as high as 50000 g's, g being the acceleration constant of gravity, in less than several milliseconds. The forces may be recorded in a Time-History (TH) diagram which plots acceleration or g's versus time. TH diagram may be transformed into a Shock Response Spectrum (SRS) which plots the shock response, in g's versus frequency, in hertz.
Pyrotechnic testing apparatus should provide predictable,repeatable and controllable SRS profiles, in particular the frequency components of the shock should be within a selected db tolerance, typically + or -3 db or 6 db for both positive and negative shock response. The testing apparatus should also be able to provide a wide range of g accelerations, in some cases as high as 10000 g's. Preferably, the test apparatus should be simple to operate, compact, transportable and without complex hammer lifting and dropping mechanisms.
Pyrotechnic shock testers can be electrodynamic shakers or drop testers or employ explosives. Electrodynamic shakers have limiting input forces and generally provide SRS profiles up to 2000 g's and 5000 hertz. Drop testers provide acceptable SRS profiles up to 6000 g's, but only in the positive direction. Explosive using testers are acceptable for 5000 g's and higher, but have their own obvious problems.
In the prior art, U.S. Pat. No. 2,799,824 discloses a shock testing device which does not provide any method to effect a change in the input frequency of the shock. U.S. Pat. No. 3,557,603 discloses a shock machine which is characterized by low acceleration levels (less than 200 g's), low frequencies (less than 200 hertz) and very low, constant deceleration levels (less than 6 g's). U.S. Pat. No. 5,003,811 discloses shock testing apparatus which provides SRS profiles approaching 10000 g's and 10000 Hertz through the use of complex beam balancing techniques to achieve desired SRS profiles for the component under test. Overall, none of the prior art apparati are compact and suitable for portability. In particular, the '811 patent describes shock testing apparatus which is at least 77 inches long, and consequently not readily transportable. Likewise, the extensive structural arrangement and weight of the prior art apparati limit their compactness and transportability.